Graz University of Technology uses communication satellites to survey the earth
By utilizing communication signals for positioning and calculating the earth’s gravitational field, real-time observation of weather phenomena is now also possible.
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Signal spectrum of the received Startlink satellite signals.
view moreCredit: IFG - TU Graz
Useable data are one of the most valuable tools scientists can have. The more data sources they have, the better they can make statements about their research topic. For a long time, researchers in the field of navigation and satellite geodesy found it regrettable that although mega-constellations with thousands of satellites orbited the Earth for communication purposes, they were unable to use their signals for positioning or for observation of the Earth. In the FFG project Estimation, the Institute of Geodesy at Graz University of Technology (TU Graz) has now conducted research on ways of utilising these signal data and thus tapping into a large reservoir of additional data sources alongside navigation satellites and special research satellites, which will help to observe changes on Earth even more precisely.
Success with the Doppler effect
Earth observation using satellites is based on the principle that changes in sea level or groundwater levels, for example, influence the Earth’s gravitational field and therefore the satellite trajectory. Scientists use this to utilise the positions and orbits of satellites as a data source for their research. “The increasing availability of satellite internet in particular means that we have a huge amount of communication signals at our disposal, which significantly exceed those of navigation satellites in terms of number and signal strength,” says Philipp Berglez from the Institute of Geodesy. “If we can now use these signals for our measurements, we not only have better signal availability, but also much better temporal resolution thanks to the large number of satellites. This also allows us to observe short-term changes. This means that, in addition to determining the position and changes in the Earth’s gravitational field that are relevant for climate research, weather phenomena such as heavy rain or changes in sea level can also be tracked in real time.”
One of the challenges in realising the project was that the satellite operators, including Starlink, OneWeb and the Amazon project Kuiper, do not disclose any information about the structure of their signals and these signals are constantly changing. In addition, there are no precise orbit data or distance measurements to the satellites, which represents potential sources of error for calculations. By analysing the Starlink signal, the researchers nevertheless found a way to enable the desired applications. They detected sounds within the signal that were constantly audible. They then utilised the Doppler effect and investigated the frequency shift of these constant tones as satellites moved towards and away from the receiver. This allowed the position to be determined with an accuracy of 54 metres. Although this is not yet satisfactory for geodetic applications, for the investigations that were carried out so far, only a fixed, commercially available satellite antenna was used to test and verify the basic principle of the measurement method.
More insight into how our world is changing
The aim now is to improve the accuracy to just a few metres. This will be made possible by antennas that can either follow the satellites or receive signals from different directions. In addition, measurements are to be taken at several locations in order to increase accuracy and reduce the influence of errors. And with more measurement data, the researchers can calculate more precise orbit data, which in turn makes determining positions and calculating the Earth’s gravitational field more accurate. The navigation working group also wants to develop new signal processing methods that filter out more precise measurement data from signals that have so far been rather unusual for geodetic applications.
“By being able to utilise the communication signals for geodesy, we have revealed enormous potential for the even more detailed investigation and measurement of our Earth,” says Philipp Berglez. “Now it’s all about improving precision. Once we have succeeded in doing this, we will be able to understand even more precisely what changes our world is undergoing. Just to be on the safe side, I would like to make the following clear: we are analysing communication signals here, but we cannot and do not want to know their content. We really only use them for positioning and observing orbits in order to determine the Earth’s gravitational field.”
Method of Research
Data/statistical analysis
Advanced seismic imaging deciphers mantle dynamics beneath Tonga subduction zone
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(a) Tectonic setting background in the Tonga-Lau-Fiji region. (b) Schematic diagram of the upper mantle structure beneath the Tonga-Lau-Fiji region.
view moreCredit: ZHAO Di, LIU Xin, ZHAO Dapeng
A landmark study published in Geoscience—a leading Chinese journal at the forefront of earth science research—has resolved critical debates about mantle dynamics beneath the Tonga Subduction Zone by unveiling its three-dimensional shear-wave velocity and azimuthal anisotropy structure. Conducted by researchers from Ocean University of China and Tohoku University, Japan, the work combines innovative seismic methodologies to map mantle flow patterns, slab-plume interactions, and back-arc basin dynamics in unprecedented detail.
The research team analyzed 150,219 amplitude and phase measurements from 1,088 teleseismic events recorded across 110 seismic stations, including land-based and ocean-bottom instruments deployed in the Lau Basin and surrounding regions. Leveraging fundamental-mode Rayleigh waves (20–150 s periods), the study applied azimuthal anisotropy tomography—a technique sensitive to directional variations in seismic wave speeds caused by aligned mineral fabrics in mantle rocks—to construct a high-resolution 3D velocity model extending to 300 km depth. Rigorous validation through checkerboard and restoring resolution tests confirmed lateral resolutions of ~150 km and vertical resolutions of 50–75 km above 150 km depth, ensuring robust spatial accuracy.
Key findings reveal that the southward influx of Samoan mantle plume material into the Lau Basin is confined to depths shallower than 50 km, driven by asymmetric rollback of the subducting Pacific Plate. This shallow flow aligns with geochemical evidence of plume-derived signatures in the basin’s northern volcanic zones. The study further identifies divergent mantle flow regimes: west-east oriented motion beneath the rapidly spreading northern Lau Basin contrasts with north-south flow in the slower southern region, reflecting passive adjustments to spatially variable slab retreat rates. Within the subducting slab, near-trench-parallel fast shear-wave directions (N-S) at shallow depths (<150 km) correlate with bending-induced normal faults, while deeper regions exhibit localized trench-perpendicular anisotropy, suggesting stress reorientation. Additionally, a trench-parallel mantle flow in the outer-rise asthenosphere—likely compressed by slab rollback—challenges conventional models of subduction-driven circulation.
The Tonga Subduction Zone, characterized by the world’s fastest plate convergence (~24 cm/year) and back-arc spreading rates, serves as a natural laboratory for studying plate-mantle interactions. By reconciling discrepancies among prior isotropic and anisotropic models, this study establishes the first cohesive 3D framework linking mantle dynamics to surface tectonics. The integration of azimuthally varying surface-wave data with multi-scale tomography represents a methodological leap, bridging geophysical observations with geochemical evidence to clarify mechanisms of mantle flow, slab-plume interplay, and back-arc basin formation. These insights not only refine understanding of subduction zone processes but also offer a template for studying other complex systems, such as the Mariana and Izu-Bonin arcs, where mantle plumes and slab dynamics similarly interact.
This research underscores the transformative potential of high-resolution seismic imaging in earth sciences. The findings highlight the importance of international collaboration in addressing geodynamic challenges, providing actionable insights for hazard mitigation and advancing predictive models of planetary-scale processes. By decoding the hidden forces shaping Earth’s interior, this work exemplifies how cutting-edge seismology can illuminate the intricate dance between tectonic plates and mantle convection—a cornerstone of modern geoscience.
Method of Research
Case study
Subject of Research
Not applicable
Article Title
Shear-wave Velocity and Azimuthal Anisotropy in the Upper Mantle of the Tonga Subduction Zone
